In a liquid crystal display, because the liquid crystal itself cannot emit light, a backlight module is used to provide a uniform light source with enough illumination to the liquid crystal panel for displaying an image. Generally, the backlight module includes an edge-illumination type and a direct-illumination type, wherein a light source of the edge-illumination is disposed at a lateral side. The edge-illumination type has advantages in light-weight, compact in size, and low power consumption, such that it has usually been used as the screen of cell phones, personal digital assistants (PDA), and notebooks.
Referring to FIG. 1, it illustrates a top view of a partial structure according to a conventional edge-illumination type backlight module. As shown in FIG. 1, the conventional edge-illumination type backlight module 9 includes a light guide plate 920 and a light emitting diode (LED) 910, wherein the LED 910 emits a light source into the light guide plate 920.
Moreover, in the conventional edge-illumination type backlight module 9, “P” represents an interval between two adjacent LEDs, “A” represents a distance form an active area 930 of a display panel projected to the light guide plate to a light emitting surface of the LED 910, and A/P ratio can be used to judge a displayed image quality. When A/P ratio is higher, the image quality is better. Otherwise, when A/P ration is lower, the image quality is poor. In the case of high A/P ratio, the light guide plate 920 can provide a more uniform light source on the active area 930 of the display panel. On the other hand, in the case of low A/P ratio, the light guide plate 920 provides a uniform light source which causes a non-uniform illumination at the local area of the active area 930, such that a hot spot is produced that lowers the image quality.
In consideration of cost, power consumption, heat-dissipating, and environment protection, the number of LEDs must be decreased; therefore, under a situation without reducing panel sizes, the interval P between the LEDs 910 may be increased. However, under a situation without reducing the active area 930 of the display panel, the distance A from the light emitting surface of the LED 910 to the active area 930 projected on the light guide plate 920 cannot be increased due to the structure limitation in the conventional backlight module 9. Hence, A/P ratio cannot be improved, and the image quality is decreased.
Thereby, a backlight module reducing hot spot appearances and the liquid crystal display using the same to solve the above-mentioned problems are required.